Neocarzinostatin (NCS), an antibiotic protein isolated from Streptomyces carzinostaticus, is in Phase I and II studies. We have been investigating several aspects of NCS and the significant results were: (a) establishment of the amino acid sequence and secondary structure of the protein, (b) preparation of biologically-active analogs, (c) development of a radioimmunoassay procedure, (d) organ and tissue distribution of NCS in normal and tumor bearing animals, and most significantly, (e) the demonstration of a possible cell surface mode of action for NCS to induce cytotoxicity in leukemic cells (CCRF-CEM) in vitro, (f) isolation of a cell line resistant to NCS. With the knowledge gained thus far, we propose to continue investigations on NCS which include: (a) chemical modification of disulfide bonds in NCS, (b) covalent coupling of NCS to albumin and soluble synthetic polymers, (c) coupling of NCS to monoclonal antibodies specific to ALL and ovarian tumors and (d) study the effect of NCS on DNA synthesis, DNA strand scission and cellular microfilaments in both normal and resistant human leukemic cell lines; these studies may result in understanding the mechanism of natural as well as induced resistance. Since NCS is suggested to have an entirely different mechanism of action compared to other anticancer agents, the investigations projected in this application may eventually lead to better clinical usage of NCS through tumor-specific binding and target-oriented transport.